/*
 * $Header: /data/cvs/alin/nanhill-platform/src/main/java/org/nanhill/commons/dbutil/BasicRowProcessor.java,v 1.1 2006/09/20 06:55:57 alin Exp $
 * $Revision: 1.1 $
 * $Date: 2006/09/20 06:55:57 $
 * 
 * ====================================================================
 *
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2002-2003 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution, if
 *    any, must include the following acknowledgement:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgement may appear in the software itself,
 *    if and wherever such third-party acknowledgements normally appear.
 *
 * 4. The names "The Jakarta Project", "Commons", and "Apache Software
 *    Foundation" must not be used to endorse or promote products derived
 *    from this software without prior written permission. For written
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache"
 *    nor may "Apache" appear in their names without prior written
 *    permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */

package org.nanhill.commons.dbutil;

import java.beans.BeanInfo;
import java.beans.IntrospectionException;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * Basic implementation of the <code>RowProcessor</code> interface. This class
 * is a thread-safe Singleton.
 * 
 * @see RowProcessor
 * 
 * @author Henri Yandell
 * @author Juozas Baliuka
 * @author David Graham
 * @author Yoav Shapira
 * @author alin
 */
public class BasicRowProcessor implements RowProcessor {

	/**
	 * Set a bean's primitive properties to these defaults when SQL NULL is
	 * returned. These are the same as the defaults that ResultSet get* methods
	 * return in the event of a NULL column.
	 */
	private static final Map<Class<?>, Object> primitiveDefaults = new HashMap<Class<?>, Object>();

	static {
		primitiveDefaults.put(Integer.TYPE, new Integer(0));
		primitiveDefaults.put(Short.TYPE, new Short((short) 0));
		primitiveDefaults.put(Byte.TYPE, new Byte((byte) 0));
		primitiveDefaults.put(Float.TYPE, new Float(0));
		primitiveDefaults.put(Double.TYPE, new Double(0));
		primitiveDefaults.put(Long.TYPE, new Long(0));
		primitiveDefaults.put(Boolean.TYPE, Boolean.FALSE);
		primitiveDefaults.put(Character.TYPE, new Character('\u0000'));
	}

	/**
	 * Special array index that indicates there is no bean property that matches
	 * a column from a ResultSet.
	 */
	private static final int PROPERTY_NOT_FOUND = -1;

	/**
	 * The Singleton instance of this class.
	 */
	private static final BasicRowProcessor instance = new BasicRowProcessor();

	/**
	 * Returns the Singleton instance of this class.
	 * 
	 * @return The single instance of this class.
	 */
	public static BasicRowProcessor instance() {
		return instance;
	}

	/**
	 * Protected constructor for BasicRowProcessor subclasses only.
	 */
	protected BasicRowProcessor() {
		super();
	}

	/**
	 * Convert a <code>ResultSet</code> row into an <code>Object[]</code>.
	 * This implementation copies column values into the array in the same order
	 * they're returned from the <code>ResultSet</code>. Array elements will
	 * be set to <code>null</code> if the column was SQL NULL.
	 * 
	 * @see org.nanhill.commons.dbutil.RowProcessor#toArray(java.sql.ResultSet)
	 */
	public Object[] toArray(ResultSet rs, int rowNum) throws SQLException {
		ResultSetMetaData meta = rs.getMetaData();
		int cols = meta.getColumnCount();
		Object[] result = new Object[cols];
		for (int i = 0; i < cols; i++) {
			result[i] = rs.getObject(i + 1);
		}
		return result;
	}

	/**
	 * Convert a <code>ResultSet</code> row into a JavaBean. This
	 * implementation uses reflection and <code>BeanInfo</code> classes to
	 * match column names to bean property names. Properties are matched to
	 * columns based on several factors: <br/>
	 * <ol>
	 * <li> The class has a writable property with the same name as a column.
	 * The name comparison is case insensitive. </li>
	 * 
	 * <li> The property's set method parameter type matches the column type. If
	 * the data types do not match, the setter will not be called. </li>
	 * </ol>
	 * 
	 * <p>
	 * Primitive bean properties are set to their defaults when SQL NULL is
	 * returned from the <code>ResultSet</code>. Numeric fields are set to 0
	 * and booleans are set to false. Object bean properties are set to
	 * <code>null</code> when SQL NULL is returned. This is the same behavior
	 * as the <code>ResultSet</code> get* methods.
	 * </p>
	 * 
	 * @see org.nanhill.commons.dbutil.RowProcessor#toBean(java.sql.ResultSet,
	 *      java.lang.Class)
	 */
	public <E> E toBean(ResultSet rs, int rowNum, Class<E> type) throws SQLException {

		PropertyDescriptor[] props = this.propertyDescriptors(type);

		ResultSetMetaData rsmd = rs.getMetaData();

		int[] columnToProperty = this.mapColumnsToProperties(rsmd, props);

		int cols = rsmd.getColumnCount();

		return this.createBean(rs, type, props, columnToProperty, cols);
	}

	/**
	 * Convert a <code>ResultSet</code> into a <code>List</code> of
	 * JavaBeans. This implementation uses reflection and <code>BeanInfo</code>
	 * classes to match column names to bean property names. Properties are
	 * matched to columns based on several factors: <br/>
	 * <ol>
	 * <li> The class has a writable property with the same name as a column.
	 * The name comparison is case insensitive. </li>
	 * 
	 * <li> The property's set method parameter type matches the column type. If
	 * the data types do not match, the setter will not be called. </li>
	 * </ol>
	 * 
	 * <p>
	 * Primitive bean properties are set to their defaults when SQL NULL is
	 * returned from the <code>ResultSet</code>. Numeric fields are set to 0
	 * and booleans are set to false. Object bean properties are set to
	 * <code>null</code> when SQL NULL is returned. This is the same behavior
	 * as the <code>ResultSet</code> get* methods.
	 * </p>
	 * 
	 * @see org.nanhill.commons.dbutil.RowProcessor#toBeanList(java.sql.ResultSet,
	 *      java.lang.Class)
	 */
	@SuppressWarnings("unchecked")
	public <E> List<E> toBeanList(ResultSet rs, Class<E> type) throws SQLException {
		if (!rs.next()) {
			return Collections.EMPTY_LIST;
		}

		List<E> results = new ArrayList<E>();
		PropertyDescriptor[] props = this.propertyDescriptors(type);
		ResultSetMetaData rsmd = rs.getMetaData();
		int[] columnToProperty = this.mapColumnsToProperties(rsmd, props);
		int cols = rsmd.getColumnCount();

		do {
			results.add(this.createBean(rs, type, props, columnToProperty, cols));

		} while (rs.next());

		return results;
	}

	/**
	 * Creates a new object and initializes its fields from the ResultSet.
	 * 
	 * @param rs
	 *            The result set
	 * @param type
	 *            The bean type (the return type of the object)
	 * @param readProperties
	 *            The property descriptors
	 * @param columnToProperty
	 *            The column indices in the result set
	 * @param cols
	 *            The number of columns
	 * @return An initialized object.
	 * @throws SQLException
	 *             If a database error occurs
	 */
	@SuppressWarnings("unchecked")
	private <E> E createBean(ResultSet rs, Class<E> type, PropertyDescriptor[] props, int[] columnToProperty, int cols)
			throws SQLException {

		E bean = (E) this.newInstance(type);

		for (int i = 1; i <= cols; i++) {

			if (columnToProperty[i] == PROPERTY_NOT_FOUND) {
				continue;
			}

			Object value = rs.getObject(i);

			PropertyDescriptor prop = props[columnToProperty[i]];
			Class propType = prop.getPropertyType();

			if (propType != null && value == null && propType.isPrimitive()) {
				value = primitiveDefaults.get(propType);
			}

			this.callSetter(bean, prop, value);
		}

		return bean;
	}

	/**
	 * The positions in the returned array represent column numbers. The values
	 * stored at each position represent the index in the PropertyDescriptor[]
	 * for the bean property that matches the column name. If no bean property
	 * was found for a column, the position is set to PROPERTY_NOT_FOUND.
	 * 
	 * @param rsmd
	 *            The result set meta data containing column information
	 * @param readProperties
	 *            The bean property descriptors
	 * @return An int[] with column index to property index mappings. The 0th
	 *         element is meaningless as column indexing starts at 1.
	 * 
	 * @throws SQLException
	 *             If a database error occurs
	 */
	private int[] mapColumnsToProperties(ResultSetMetaData rsmd, PropertyDescriptor[] props) throws SQLException {

		int cols = rsmd.getColumnCount();
		int columnToProperty[] = new int[cols + 1];

		for (int col = 1; col <= cols; col++) {
			String columnName = rsmd.getColumnName(col);
			for (int i = 0; i < props.length; i++) {

				if (columnName.equalsIgnoreCase(props[i].getName())) {
					columnToProperty[col] = i;
					break;

				} else {
					columnToProperty[col] = PROPERTY_NOT_FOUND;
				}
			}
		}

		return columnToProperty;
	}

	/**
	 * Convert a <code>ResultSet</code> row into a <code>Map</code>. Every
	 * key in the return <code>Map</code> is lowercase.
	 * 
	 * @see org.nanhill.commons.dbutil.RowProcessor#toMap(java.sql.ResultSet)
	 */
	public Map<String, Object> toMap(ResultSet rs, int rowNum) throws SQLException {
		ResultSetMetaData rsmd = rs.getMetaData();
		int cols = rsmd.getColumnCount();
		Map<String, Object> result = new HashMap<String, Object>(cols);
		for (int i = 1; i <= cols; i++) {
			result.put(rsmd.getColumnName(i).toLowerCase(), rs.getObject(i));
		}
		return result;
	}

	/**
	 * Calls the setter method on the target object for the given property. If
	 * no setter method exists for the property, this method does nothing.
	 * 
	 * @param target
	 *            The object to set the property on.
	 * @param prop
	 *            The property to set.
	 * @param value
	 *            The value to pass into the setter.
	 * @throws SQLException
	 *             if an error occurs setting the property.
	 */
	private void callSetter(Object target, PropertyDescriptor prop, Object value) throws SQLException {

		Method setter = prop.getWriteMethod();

		if (setter == null) {
			return;
		}

		Class<?>[] params = setter.getParameterTypes();
		try {
			// Don't call setter if the value object isn't the right type
			if (this.isCompatibleType(value, params[0])) {
				setter.invoke(target, new Object[] { value });
			}

		} catch (IllegalArgumentException e) {
			throw new SQLException("Cannot set " + prop.getName() + ": " + e.getMessage());

		} catch (IllegalAccessException e) {
			throw new SQLException("Cannot set " + prop.getName() + ": " + e.getMessage());

		} catch (InvocationTargetException e) {
			throw new SQLException("Cannot set " + prop.getName() + ": " + e.getMessage());
		}
	}

	/**
	 * ResultSet.getObject() returns an Integer object for an INT column. The
	 * setter method for the property might take an Integer or a primitive int.
	 * This method returns true if the value can be successfully passed into the
	 * setter method. Remember, Method.invoke() handles the unwrapping of
	 * Integer into an int.
	 * 
	 * @param value
	 *            The value to be passed into the setter method.
	 * @param type
	 *            The setter's parameter type.
	 * @return boolean True if the value is compatible.
	 */
	private boolean isCompatibleType(Object value, Class<?> type) {
		// Do object check first, then primitives
		if (value == null || type.isInstance(value)) {
			return true;

		} else if (type.equals(Integer.TYPE) && Integer.class.isInstance(value)) {
			return true;

		} else if (type.equals(Long.TYPE) && Long.class.isInstance(value)) {
			return true;

		} else if (type.equals(Double.TYPE) && Double.class.isInstance(value)) {
			return true;

		} else if (type.equals(Float.TYPE) && Float.class.isInstance(value)) {
			return true;

		} else if (type.equals(Short.TYPE) && Short.class.isInstance(value)) {
			return true;

		} else if (type.equals(Byte.TYPE) && Byte.class.isInstance(value)) {
			return true;

		} else if (type.equals(Character.TYPE) && Character.class.isInstance(value)) {
			return true;

		} else if (type.equals(Boolean.TYPE) && Boolean.class.isInstance(value)) {
			return true;

		} else {
			return false;
		}

	}

	/**
	 * Returns a new instance of the given Class.
	 * 
	 * @param c
	 *            The Class to create an object from.
	 * @return A newly created object of the Class.
	 * @throws SQLException
	 *             if creation failed.
	 */
	private Object newInstance(Class<?> c) throws SQLException {
		try {
			return c.newInstance();

		} catch (InstantiationException e) {
			throw new SQLException("Cannot create " + c.getName() + ": " + e.getMessage());

		} catch (IllegalAccessException e) {
			throw new SQLException("Cannot create " + c.getName() + ": " + e.getMessage());
		}
	}

	/**
	 * Returns a PropertyDescriptor[] for the given Class.
	 * 
	 * @param c
	 *            The Class to retrieve PropertyDescriptors for.
	 * @return A PropertyDescriptor[] describing the Class.
	 * @throws SQLException
	 *             if introspection failed.
	 */
	private PropertyDescriptor[] propertyDescriptors(Class<?> c) throws SQLException {
		// Introspector caches BeanInfo classes for better performance
		BeanInfo beanInfo = null;
		try {
			beanInfo = Introspector.getBeanInfo(c);

		} catch (IntrospectionException e) {
			throw new SQLException("Bean introspection failed: " + e.getMessage());
		}

		return beanInfo.getPropertyDescriptors();
	}

}
